Year	mmol per litre
1980	5.558
1981	5.542
1982	5.523
1983	5.5
1984	5.478
1985	5.452
1986	5.428
1987	5.405
1988	5.385
1989	5.369
1990	5.354
1991	5.341
1992	5.333
1993	5.324
1994	5.316
1995	5.309
1996	5.302
1997	5.3
1998	5.3
1999	5.3
2000	5.299
2001	5.294
2002	5.288
2003	5.282
2004	5.277
2005	5.271
2006	5.265
2007	5.26
2008	5.252